1. Field of the Invention.
The field of the invention is anti-theft device for semi-truck trailers.
2. Description of Related Art.
One of the problems with attempting to secure semi-truck trailers against theft is that the trailers are so amenable to being stolen. The convenience and relative ease of attaching and detatching a semi-truck tractor to the trailer also provides the convenience and ease by which to steal the trailer. Most, if not all, trailers and tractors utilize a so-called "fifth wheel" type lubricated flat swivel plate and catch assembly mounted on the tractor to engage a corresponding lubricated flat swivel plate and downward protruding "king pin" situated on the underside of the forward portion of the trailer. The trailer's king pin rides into a slot in the tractor swivel plate where it engages the catch assembly to be locked into place.
The trailer, absent the tractor, rests horizontally upon its rear wheels and upon the front landing gear.
Once a tractor has engaged the trailer swivel plate and king pin assembly, the trailer's landing gear is raised, and then the tractor may be driven off pulling the trailer behind it.
The landing gear conventionally comprises a pair of spaced apart concentric cylinders where the inner cylinder telescopes out of the outer cylinder to meet the ground. In most cases, the lower end of the inner cylinder is fitted with a metal flat plate "foot" for purposes of engaging the ground when the landing gear is in its extended down position and the trailer is separated from the tractor to stand by itself. To raise the landing gear, mechanical ratchet means are incorporated in the landing gear assembly by which the inner cylinders of the landing gear are telescoped into the outer cylinders and the inner cylinders with the foot are raised out of the way so that the trailer may be pulled without interruption. There may be separate mechanical ratchet means on each of the pair of concentric cylinders or a connecting rod may join the two ratchets together.
In most instances the landing gear is initially set while the trailer is still being supported by the tractor so that the landing gear will support the trailer after the tractor is driven out from under the front portion of the trailer.
If the trailer were to be pulled by a tractor with the landing gear still extended where the tractor's fifth wheel had raised the trailer's front portion slightly above the landing gear's resting position which would be the usual position where the landing gear is set in the instance just above, failure to retract the landing gear would result in the landing gear striking the least elevated spot in the road and interfering substantially with movement of the trailer from being moved over anything but an absolutely smooth road. If the height of the forward portion of the trailer in its resting position upon the landing gear were such that it were higher than the fifth wheel of the tractor, then it may be impossible for the tractor to secure the trailer without lowering the landing gear or railing the tractor. In any event, movement under either case would be impossible without substantially dragging of the landing gear.
Accordingly, it is obvious that if the unauthorized retraction of the landing gear can be prevented, a substantial anti-theft measure has been provided against unauthorized removal of a trailer. If the landing gear can not be retracted, then either engagement of the trailer by a tractor is rendered impossible without additional time consuming measures taken or movement of the trailer is rendered substantially more difficult.
Obviously then theft of the trailer is prevented against all but the most determined and best equipped thieves.
The Inventor is not knowledgeable of any other devices which renders a trailer landing gear selectively inoperable as an anti-theft measure, however, the Inventor is aware of measures which have been taken by other parties to similarily prevent theft of semi-truck trailers. For example, Stone et al, in U.S. Pat. No. 3,982,413 provides a lock which is adapted to surround the trailer "king pin" such as to effectively increase the shaft diameter of the king pin to a size that will not move into the slot of a semi-truck tractor "fifth wheel" swivel plate.